Mark some exception classes as SAL_WARN_UNUSED

...so that it would have found 09978dd1
"clang-tidy bugprone-unused-return-value"

Change-Id: I75fb36618bf76110e5c32b9c2a5aeff7461a2a9a
Reviewed-on: https://gerrit.libreoffice.org/60235
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

include/unoidl/unoidl.hxx

@@ -24,7 +24,7 @@
 
 namespace unoidl {
 
-class LO_DLLPUBLIC_UNOIDL NoSuchFileException final {
+class LO_DLLPUBLIC_UNOIDL SAL_WARN_UNUSED NoSuchFileException final {
 public:
     SAL_DLLPRIVATE NoSuchFileException(rtl::OUString const & uri): uri_(uri) {}
 
@@ -41,7 +41,7 @@ private:
     rtl::OUString uri_;
 };
 
-class LO_DLLPUBLIC_UNOIDL FileFormatException final {
+class LO_DLLPUBLIC_UNOIDL SAL_WARN_UNUSED FileFormatException final {
 public:
     SAL_DLLPRIVATE FileFormatException(
         rtl::OUString const & uri, rtl::OUString const & detail):